It should be noted that, at least regarding the current invention, metrology instruments include measuring instruments arranged to determine coordinates or relative positions of predetermined points of interest using photonic beams and rays (visible, infrared, ultraviolet, x rays, gamma rays, microwaves, radio waves), particulate beams (including electron and positron beams, neutron beams, pion (charged and neutral) beams, meson (charged and neutral) beams, ion beams, atomic and polyatomic beams, molecule beams, and combinations including neutral and charged plasma beams and jets, and/or beams and streams of aggregated structures (including but not limited to, colloidal complexes, mono and poly crystals, nanotubes, fullerenes, glassy aggregates and combination structures).
Consequently, a particular subset of optical metrology instruments may include Laser Radars (LR), Laser Trackers (LT), optical directional and rangefinders, optical imagers and cameras, optical scanners, laser levels and plane finders, goniometers, theodolites, clinometers, tiltmeters, optical sights, optical markers and designators, and/or combination metrology instruments combining structures and functionalities of the listed instruments.
In particular embodiments, optical metrology instruments such as LR or LT may have measurement accuracies on the order of 0.025 mm over a 2 m measurement range when used in ambient conditions with no window between the measurement instrument and the target. When these same instruments are used to measure targets through a thick dielectric window without correcting for window effects measurement error will be on the order of the thickness of the single-pass glass path. Consequently, measurements made through a window, without applying the necessary corrections may result in suboptimal measurements.
In different classes of embodiments addressing situations where the metrology instrument and object to be measured may be separated by a stratified medium because of environmental, safety, contamination, or packaging requirements, etc. could potentially use the LRTW correction capability. One such example may consider accurate remote measurements and recordings of positions of parts (e.g. fuel roads) inside nuclear reactors trough windows, cooling fluids, and/or moderating fluids.
Prior to the development of the LRTW coordinate correction method, correction of LRTW measurements have been performed generally using commercial ray trace methods and software usually augmented with custom scripts. Frequently, however, making through-the-window measurements with metrology instruments such as the LR or LT was avoided altogether.
Commercial ray trace methods and software packages may be costly and post-processing of the ray trace results may still be required. Also, calling commercial ray trace applications from a commercial metrology application, although possible, may involve additional overhead for importing/exporting the data and for running uncompiled scripts.
The LRTW correction software of the current invention may be integrated into commercial metrology software to allow targets measured through a window to be corrected in seconds to give the user real-time feedback. This LRTW correction software offers a complete solution for correcting all range and pointing errors associated with measuring targets through a window. Also, costly commercial ray trace software may not be required since this functionality may be an integral function of the LTRW software.
The LRTW coordinate correction method may also be used in a reverse mode to calculate apparent point of interest coordinates for known or corrected targets measured through a window. The apparent point of interest coordinates refers to the instrument reported coordinates when no window, vacuum, or SGR corrections have been applied. This capability may be useful for allowing the metrology instrument to locate targets measured through a window based on ambient blue print values to within 0.050 mm. Without this capability the time required to locate the targets manually could increase substantially as targets inside a vacuum chamber may not be well illuminated and may be difficult to locate, especially when viewing through the built-in LR or LT camera.
Some aspects and issues related to the subject matter of current invention have been addressed in the following nonpatent publications, incorporated herein by reference:
T. Hadjimichael et. al. in “Cryogenic metrology for the James Webb Space Telescope Integrated Science Instrument Module alignment target fixtures using laser radar through a chamber window”, Proc of SPIE Vol. 7793.
B. Eegholm, T. Hadjimichael, J. Hayden, R. Ohl, D. Kubalak, R. Telfer, “Laser Radar Through the Window (LRTW) Coordinate Correction Software”, Sigma Space Invention Disclosure, filed Nov. 4, 2010.